FAIR VALUE MEASUREMENTS - Recurring Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Liabilities
Restricted cash	$ 49	$ 67
Investment excludes receivables, payables and accrued income		1
Recurring
Assets
Fair value, assets	1,837	2,123
Liabilities
Fair value, liabilities	(1)	0
Net assets (liabilities)	1,836	2,123
Recurring \| FTRs \| Derivative Liabilities
Liabilities
Fair value, liabilities	(1)	0
Recurring \| FTRs \| Derivative Assets
Assets
Fair value, assets	9	3
Recurring \| Equity securities
Assets
Fair value, assets	2	2
Recurring \| Cash, cash equivalents and restricted cash
Assets
Fair value, assets	1,511	1,801
Recurring \| U.S. state debt securities
Assets
Fair value, assets	273	276
Recurring \| Other
Assets
Fair value, assets	42	41
Recurring \| Level 1
Assets
Fair value, assets	1,513	1,803
Liabilities
Fair value, liabilities	0	0
Net assets (liabilities)	1,513	1,803
Recurring \| Level 1 \| FTRs \| Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Recurring \| Level 1 \| FTRs \| Derivative Assets
Assets
Fair value, assets	0	0
Recurring \| Level 1 \| Equity securities
Assets
Fair value, assets	2	2
Recurring \| Level 1 \| Cash, cash equivalents and restricted cash
Assets
Fair value, assets	1,511	1,801
Recurring \| Level 1 \| U.S. state debt securities
Assets
Fair value, assets	0	0
Recurring \| Level 1 \| Other
Assets
Fair value, assets	0	0
Recurring \| Level 2
Assets
Fair value, assets	315	317
Liabilities
Fair value, liabilities	0	0
Net assets (liabilities)	315	317
Recurring \| Level 2 \| FTRs \| Derivative Liabilities
Liabilities
Fair value, liabilities	0	0
Recurring \| Level 2 \| FTRs \| Derivative Assets
Assets
Fair value, assets	0	0
Recurring \| Level 2 \| Equity securities
Assets
Fair value, assets	0	0
Recurring \| Level 2 \| Cash, cash equivalents and restricted cash
Assets
Fair value, assets	0	0
Recurring \| Level 2 \| U.S. state debt securities
Assets
Fair value, assets	273	276
Recurring \| Level 2 \| Other
Assets
Fair value, assets	42	41
Recurring \| Level 3
Assets
Fair value, assets	9	3
Liabilities
Fair value, liabilities	(1)	0
Net assets (liabilities)	8	3
Recurring \| Level 3 \| FTRs \| Derivative Liabilities
Liabilities
Fair value, liabilities	(1)	0
Recurring \| Level 3 \| FTRs \| Derivative Assets
Assets
Fair value, assets	9	3
Recurring \| Level 3 \| Equity securities
Assets
Fair value, assets	0	0
Recurring \| Level 3 \| Cash, cash equivalents and restricted cash
Assets
Fair value, assets	0	0
Recurring \| Level 3 \| U.S. state debt securities
Assets
Fair value, assets	0	0
Recurring \| Level 3 \| Other
Assets
Fair value, assets	$ 0	$ 0

Fair value of assets and liabilities net.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Fair value of financial and nonfinancial obligations.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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